1. Field of the Invention
The invention relates to a medium containing cassette for containing recording media to be fed by a paper feeding mechanism in an image forming apparatus, a medium feeding unit incorporating the medium containing cassette, an optional medium feeding unit such as an optional tray unit incorporating the medium containing cassette and an image forming apparatus incorporating the medium containing cassette, the medium feeding unit or the optional medium feeding unit and configured to develop images according to received image data on the recording medium and output them.
2. Description of Related Art
Regarding a conventional image forming apparatus such as a copying machine, a printer, facsimile machine or electrophotographic color recording machine, a charging roller uniformly charges a photosensitive drum serving as an image carrier, an exposure unit directly exposes the photosensitive drum or indirectly exposes the photosensitive drum using a laser scanning optical system or a LED recording optical system so as to form an electrostatic latent image according to image information on the photosensitive drum, a developer supply unit supplies toner serving as a developer to a developer carrier, the developer carrier develops the electrostatic latent image to form a toner image on the photosensitive drum by supplying the toner to the photosensitive drum directly or indirectly via an intermediate transferring member, a transfer unit transfers the toner image formed on the photosensitive drum onto a recording medium serving as a printable sheet such as paper, film or the like, and then a fixing unit melts and presses the toner image transferred on the recording medium to fix the toner image on the recording medium.
Such an image forming apparatus includes a medium containing cassette which contains the recording media in a stacked manner to be fed by the medium feeding roller mechanism serving as a medium feeding mechanism of a medium conveying unit. The medium containing cassette includes, a stack plate on which the recording media are stacked, a spring attached under the stack plate serving as a bias member which biases the stack plate toward the medium feeding roller mechanism of the medium conveying unit, a separating pad opposed to the medium feeding roller mechanism of the medium conveying unit and configured to separate the stacked recording media so as to feed one recording medium at a time, side end guide members configured to line up the side ends of the stacked recording media, and a rear end guide member provided on the side opposed to the separating pad and configured to line up the rear end of the stacked recording media.
When the medium containing cassette containing the recording media is attached to the image forming apparatus, the stack plate is lifted up by the biasing force of the spring that is attached under the stack plate so that the uppermost recording medium is in press contact with the medium feeding roller of the medium feeding roller mechanism. The stacked recording media to be fed by a rotation of the medium feeding roller are separated one by one by the separating pad and then conveyed downstream of the recording medium conveying path (for example, Japanese Patent Application Laid-Open No. H08-324804).
In the described configuration, the medium containing cassette needs to have a certain height that is the sum of the height of the stack of recording media, the thickness of the stack plate on which the stack of recording media is placed, the height of the compressed spring that biases the stack plate, and the height of a spring seating portion of the bottom of the medium containing cassette having enough strength to tolerate the compression bias force of the spring.